It was narrated from Ya'la bin Murrah that his father said:
"I was with the Prophet on a journey, and he wanted to relieve himself. He said to me: 'Go to those two small date-palm trees and tell them: "The Messenger of Allah orders you to come together.'" So they came together and he concealed himself behind them, and relieved himself. Then he said to me: 'Go to them and tell them: "Go back, each one of you, to your places.'" So I said that to them and they went back." (DE)
English reference (DE): Vol. 1, Book 1, Hadith 339 (DE)
Arabic reference (DE): Book 1, Hadith 363 (DE)